Sintering process



Patented Oct. 5, 1954 SINTERING PROCESS Kiirt Meyer, Frankfurt am Main, Germany, as-

signor to Metallgesellschaft Aktiengesellschaft, Frankfurt am Main, Germany, a corporation of Germany No Drawing. Application October 18, 1950, Serial No. 190,885

Claims priority, application Germany October 31, 1949 Claims.

This invention relates to a sintering process and has particular reference to certain improvements in the known process of sintering under action of a blast of air, more particularly of an induced draught. Said process is used mainly for agglomerating fine-grained iron ore, or for the sintering and roasting of sulphides of the non-ferrous metals and for the production of hydraulic binders.

Also, many times it has been attempted to apply the expedient of adding alkali salts as a decomposing agent for the decomposition Oif alumina compounds, e. g. bauxites or phosphates or the like.

These attempts so far were not really successful, since it was not possible to keep the fuel burning, even if it was ignited by a suitable igniting flame within the charge.

It is an object of the present invention to remove these difiiculties in sintering processes of the type referred to.

According to the present invention it has been found that these sintering processes apart from other difficulties are disturbed by the premature occurring of low-melting substances, more particularly by action of the alkali salts, such as Na-zCOs, NA2SO4, K2804 and others, as well as of alkaline earth salts, such as bitter salts or magnesium sulphate, or calcium chloride, because these substances practically render the combustion of the coke impossible. These and other soluble salts have the eifect of impeding the combustion of the coke. Furthermore, it was found, that these detrimental actions can be restrained by suitable additions and measures. A particularly efiective expedient in this respect proved to be the .step of moistening or wetting the fuels used for the sintering, e. g., coke; and then to mix them with quicklime, which thereby is transformed into hydrate of lime, and by the expansion of its volume closes the pores of the coke or the like largely against the penetration of dissolved salts and low-melting substances. The hydrate of lime thus prevents these melts and solutions from penetrating into the coke grain when moistening and crumbling the charge for the sintering grate and during the sintering, and in its turn reacts with the disturbing substances, e. g. soluble carbonates or sulphates, as the case may be. It is also possible to use, instead of quicklime or slaked lime, other oxides, such as burnt dolomite, alumina, finely ground clay or the like.

Example 1 kgs. of ground pebble-phosphate are mixed with 6 kgs. of soda and 1.5 kgs. of coke, crumbled and exposed to the sintering process on the blast grate. The product of the burning process besides much unburnt coke contains a considerable share of unsintered mixture. The solubility in citric acid of the P205 determined in the sintered parts is about percent. On the other hand, if the coke advantageously moistened preliminarily is mixed with 1 kg. of quicklime and this mixture is crumbled with the phosphate and the soda, in accordance with the preesnt invention, the sintering under action of an air blast takes place without disturbance. The share of P205 soluble in citric acid rises to 97 to 98 percent. There were hardly any unsintered parts. The latter can be used as waste or return material and worked up in known manner.

Example 2 A mixture of 100 parts of bauxite with 62 parts of calcined soda and 14 parts of coke were crumbled and sintered on the blast grate. Apart from a considerable amount of non-sintered parts of the charge, only 81.5 percent of the alumina contained in the bauxite were transformed into a soluble form. On the other hand, if in case of the same charge 10 parts by weight of hydrate of lime are additionally mixed to the coke and the mixture is then crumbled, in accordance with the present invention, a uniformly sintered-through product was obtained, and the solubility was raised to 93.7%.

While the invention has been described in detail with respect to certain now preferred examples and embodiments of the invention it will be understood by those skilled in the art after understanding the invention, that various changes and modifications may be made without departing from the spirit and scope of the invention and it is intended, therefore, to cover all such changes and modifications in the appended claims.

What is claimed is:

1. In a process of sintering under the action of a blast of air, a material to be decomposed selected from the group consisting of phosphates and bauxite in admixture with a solid carbonaceous, relatively porous fuel and a decomposing agent selected from the group consisting of watersoluble alkali metal and alkaline earth metal salts, the steps which comprise mixing said fuel in a wet condition with a substance capable of removing the combustion impeding efiect of the decomposing agent, said substance selected from the group consisting of burnt lime, slaked lime, burnt dolomite, and alumina before such fuel is 3 4 admixed with said decomposing agent, adding the 5. In a process of sintering as in claim 1, said decomposing agent, and then sintering the mixmaterial to be decomposed being phosphate rock. ture.

2. In a process as in claim 1, the substance Re s Cited in fi s Patent capable of removing'the combustion impeding 5 UNITED STATES PATENTS efiect of the decomposing agent being burnt lime.

3. In a process of sintering as in claim 1, said Number Name Date fuel being coke and said decomposing agent 108,089 Bfiker 111 1870 being odium carbonate. 2,372,819 Flsber p 1945 4. In a process of sintering. as-inclaim I, said 10 23394393 Maler material to be decomposed being bauxite. 250L952 Maier 1950 

1. IN A PROCESS OF SINTERING UNDER THE ACTION OF A BLAST OF AIR, A MATERIAL TO BE DECOMPOSED SELECTED FROM THE GROUP CONSISTING OF PHOSPHATES AND BAUXITE IN ADMIXTURE WITH A SOLID CARBONACEOUS, RELATIVELY POROUS FUEL AND A DECOMPOSING AGENT SELECTED FROM THE GROUP CONSISTING OF WATERSOLUBLE ALKALI METAL AND ALKALINE EARTH METAL SALTS, THE STEPS WHICH COMPRISES MIXING SAID FUEL IN A WET CONDITION WITH A SUBSTANCE CAPABLE OF REMOVING THE COMBUSTION IMPEDING EFFECT OF THE DECOMPOSING AGENT, SAID SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF BURNT LIME, SLAKED LIME, BURNT DOLOMITE, AND ALUMINA BEFORE SUCH FUEL IS ADMIXED WITH SAID DECOMPOSING AGENT, ADDING THE DECOMPOSING AGENT, AND THEN SINTERING THE MIXTURE. 